1. Technical Field
The present invention relates to an elastic boundary wave substrate on which energy is concentrated into a substrate surface thereof and an electrode section, so as to be propagated, and an elastic boundary wave functional element using the substrate.
2. Background Art
Elastic surface wave filters and elastic surface wave functional elements each using an elastic surface wave converter wherein an interdigital electrode is set on a piezoelectric substrate are widely used as intermediate frequency band filters for television or filters for mobile communication. In these filters, an elastic surface wave is used; thus, their surface for propagating and receiving the elastic surface wave and their propagation path surface need to be made free. Thus, these filters are each required to be packaged. In the meantime, by use of an elastic boundary wave, the energy of which is confined in a substrate, a functional element for which no package is necessary can be attained. A first research article wherein an elastic boundary wave is analyzed is R. Stoneley: R. Soc. Proc. London Ser. A., 106 (1924) 416. An article on a combination of a piezoelectric substrate with a thin film is K. Yamanouchi, K. Iwahashi and K. Shibayama, “Piezoelectric Boundary Waves along the Interface between SiO2 and LiTaO3”, IEEE Transactions Sonics and Ultrasonics, Vol. SU-25, No. 6, 1978, pp. 384-389. According to this article, only a monolayered thin film is used so that conditions for trapping a boundary wave into a boundary are strict. As a result, the combination has not been put into practical use.
The present patent has been made in order to overcome these drawbacks.